The armed forces of many nations have, at one time or another, used foreign volunteers who are motivated by political or ideological considerations to join a foreign army. These may be formed into units of a given nationality or may be formed into mixed nationality foreign units. Sometimes foreign volunteers were or are incorporated into ordinary units.

Mixed nationality units of foreign volunteers

• French Foreign Legion
• International Brigades of the Spanish Civil War
• Tercio de Extranjeros, or Tercio, or Spanish Legion (prior to 1987)
• Rhodesian Light Infantry (initially all-Rhodesian, this unit became the "Foreign Legion" of the Rhodesian Army)
• Many members of the US Marine Corps are of Latin American and not US nationality. The US Army made extensive use of foreign soldiers, particularly Irish and German, during the nineteenth century; German Jewish troops were common during World War II. However, many if not most non-American troops in the United States armed forces are usually seeking the expedited United States citizenship that comes with completion of a term of service, and can be seen as aspiring Americans rather than outright foreigners.
• The German SS (particularly the Waffen-SS) made extensive use of foreigners during World War II. For more information, see: Europäische Freiwillige, Foreign volunteers and conscripts in the Waffen-SS.

Units of foreign volunteers of specific nationality

American

• The Lafayette Escadrille in the French Air Force, World War I
• The Eagle Squadrons in the Royal Air Force, World War II
• The Flying Tigers in the Chinese Air Force, World War II
• Before the US entered the war, many Americans joined the Canadian armed forces, especially the RCAF, and served in ordinary Canadian units.

British

• The British Legions in the South American Wars of Independence during the 19th century.

French

• Some French emigres who fled to Britain fought in the British Army of the Napoleonic Wars
• Charlemagne Regiment of the SS fought for Germany in the Second World War

German

• King's German Legion in the Napoleonic Wars
• Condor Legion in the Spanish Civil War
• Hessians - Germans who fought for the British during the American Revolution

Irish

• The Irish Brigade in the French Army from 1690 and through the eighteenth century.
• An Irish Legion was part of the British Legions fighting in the South American Wars of Independence
• St. Patrick's Battalion in the Mexican Army during the Mexican-American War.
• The Irish Brigade which served on the Union side in the American Civil War in the 1860s
• Irish commandos in the Boer Army during the Boer War
• The Irish Brigade which fought on the Nationalist side in the Spanish Civil War

International

• The International Brigades in the Spanish Civil War

Italian

• The Redshirts of Giuseppe Garibaldi fought in Southern Italy and Uruguay.
• Corpo Truppe Volontarie in the Spanish Civil War.

Nepalese

• Gurkhas in the British Army.
• Gorkhas in the Indian Army.

Morrocan

• Fuerzas Regulares Indígenas in the Spanish Civil War

Palestine

• Palestine Liberation Army - an auxiliary of the Syrian Army

Polish

• Brigades in the Spanish Civil War.
• Polish Lancers and other Polish forces in the Army of Napoleon.

Portuguese

• Legião Viriato in the Spanish Civil War.

Scottish

South Africa

• South African 32 Battalion

Spanish

• The Blue Division of World War II fighting against the USSR.
• The Blue Legion was formed late in the Second World War out of Blue Division soldiers who refused to leave after Franco required all Spaniards to leave Axis forces.
• The 9th Armoured Company of the Free French Forces.
• The Spanish Legion accepts foreign recruits from Spanish speaking Central and South America.

Swedish

• Swedish Voluntary Air Force fighting for the Finnish side in the Winter War
• Swedish Volunteer Corps fighting for the Finnish side in the Winter War

See also

• Spanish Civil War and Foreign Involvement
• Mercenary
• Europäische Freiwillige of the Second World War
• Military volunteer